The Biology of Polyporus Pargamenus Fries 169 
Polyporus pargamenus as a sap-rotting fungus is espe- 
cially notorious for attacking those ties, timbers, and logs 
from which the bark has not been removed. The rapidity 
with which felled trees may be attacked and rotted by this 
fungus is a factor that must be taken into account when 
logging hardwoods, especially in the Southern Appalachian 
region. The destruction of the sapwood by this and other 
sap-rotting fungi often is so serious that unusual means often 
must be resorted to in order to get logs out of the woods 
before their value depreciates materially. Ordinarily the 
trees are attacked by a large number of sap-rotting fung) 
very shortly after they are felled, particularly if they are 
cut in the months from March to October. The rate of the 
destruction of the sapwood by these fungi varies greatly, 
however, according to the durability of the respective woods 
in question. 
The decay which Polyporus pargamenus brings about in 
wood is usually confined for a year or more to the sapwood, 
and in many species it is largely confined to the sapwood. 
This is true of such trees that have their heartwood sharply 
differentiated from their sapwood as in the oaks. It is only 
after the sapwood is completely decayed that the heartwood 
is attacked to any great extent. Even then it is decayed 
far more slowly than the sapwood due to its greater dur- 
ability. The manner and extent of the decay, of course, 
varies greatly not only with the species of tree, but also with 
the development of heartwood and its chemical and physical 
qualities. In the woods where the differentiation between 
the heartwood and sapwood is indistinct, as in the willows, 
poplars and birches, the fungus brings about the destruction 
of the sapwood with great rapidity and even destroys the 
heartwood with almost, if not equal, celerity. This varia- 
tion is to be attributed to the greater durability possessed by 
_the woods having a deep-colored heartwood and is due to the 
greater infiltrations of tannins, oils, and resins which render 
the wood more resistant to decay-producing fungi. The rate 
at which the sapwood of different dicotyledonous species 
decays presents little variation. The rate at which the heart- 
